This invention relates to a process for the prevention of marine encrustation on components used in a marine environment and in particular although not exclusively bronze or copper components, such as bronze propellers. Bronze includes tin bronze, aluminium bronze, silicon-aluminium bronze, nickel-aluminium bronze and manganese bronze.
A problem with components that are submerged in a marine environment for extended periods is that marine life encrustation can develop on the surface of the component. This is particularly a problem with propellers. In operation, water travels over the propeller blades at high velocity, it is essential for the efficiency of the propeller, that the surface be perfectly smooth, even and true. From the time that they are immersed into a marine environment, bronze propellers are prone to attack by marine organisms, such as barnacles, coral and algae, which attach themselves to the bronze metallic surface, creating lumps on the propeller, which adversely affect its balance and cause impedance and vibration of the propeller and its boat in the water. Various remedies have been tried including anti-fouling paints. One of these paints containing tributyl tin, was so toxic to other economic marine life, such as oysters, that it had to be discontinued. Its successor is so aggressive, that its application to the finely polished surface of the bronze leaves brush marks in the form of grooves, that adversely affect the fine balance and vibration free performance of the propeller. Durability of the anti-fouling paint on the propeller can be as short as 30 days in active marine environments.
Accordingly, the inventive process seeks to provide protection from marine encrustation for an extended period of time.
In accordance with the present invention there is provided a process for improving the resistance to marine encrustation of a component used in a marine environment, including the step of treating the component with a hypochlorite or a hypochlorite-containing material or a precursor thereof.
Preferably, the component is made from copper, contains copper or is provided with a surface layer of copper or copper-containing material. More preferably, the process further includes forming a layer of copper or copper-containing material on the surface of the component before treatment by the hypochlorite material, particularly if the surface of the component is not copper or is not provided with a copper or copper-containing surface.
Preferably, the hypochlorite material is a hypochlorite salt solution or a material capable of forming a hypochlorite salt solution.
Preferably, a cupric chloride coating is formed on the surface of the component by treating the copper surface or copper surface layer of the component with the hypochlorite salt solution.
Preferably, the component is metallic and the copper layer is formed on the metallic surface by electroplating. More preferably, the copper layer is formed to a minimum depth of 0.06 millimetres. Typically the component or the surface of the component is or includes bronze before being electroplated with copper.
Preferably, a process according to claim 6, wherein the bronze surface is cleansed before electroplating.
Preferably, the copper surface is exposed to the hypochlorite salt solution for a period of time sufficient for the basic cupric chloride coating to form.
Preferably, the hypochlorite salt solution is a standard sodium hypochlorite solution containing 5% sodium hypochlorite and 5% sodium chloride.
Preferably, the hypochlorite salt solution is applied, preferably sprayed onto the copper surface or copper layer.
Preferably, the surface of the component is polished before it is cleansed.
Preferably, the step of forming the basic cupric chloride coating is preceded by the formation of cupric oxide.
Preferably, the component is a bronze propeller. More preferably, the bronze propeller is a newly cast bronze propeller that has been first polished to propeller production standard. Preferably, wherein the polishing procedure incudes using a 60# grit size at 3500 sfm for roughing, followed by using a 180# grit size at 5500 sfm for finishing the propeller using grease as a polishing aid.
Preferably, the surface cleansing includes one or more steps of alkaline cleaning by dipping or electrolytic means, vapour degreasing and solvent cleaning.
Preferably, the copper layer is electroplated using an electroplating bath which is alkaline. More preferably, the copper electroplating bath is an alkaline cyanide bath. Alternatively, the copper electroplating bath is an alkaline pyrophoshate bath.
Alternatively, the copper layer is electroplated using an electroplating bath which is acid. Preferably, the copper electroplating bath is an acid sulphate bath. Preferably, the copper electroplating bath is an acid fluoborate bath.
In accordance with another aspect of the present invention there is provided a component having increased resistance to marine encrustation in a marine environment, wherein the surface of the component has been treated with a hypochlorite or hypochlorite-containing material or precursor thereof, after which the component is provided with a basic cupric chloride coating.
Preferably, the component is made from copper, contains copper or is provided with a surface layer of copper or copper-containing material on which the basic cupric chloride coating is formed. More preferably, the copper or copper-containing surface is a layer formed on a metallic surface of the component. Still more preferably, the metallic surface is a bronze surface of the component: Typically, the component is a bronze propeller.
Preferably, the layer is an electroplated layer.
Preferably, the basic cupric chloride coating is a cupric oxy-chloride coating. More preferably, the basic cupric chloride coating is a cupric chloro-hypochlorite coating.